iTunes sales has iPad sales beat by 2% in the overall revenue pie for Apple. That's a 40% advantage iTunes enjoys over iPod sales. Not long ago, iPod was king. It was the single device that saved Apple and launched Apple's domination in mobile.
More importantly, iTunes content could be future drivers at Apple. Right now, all the focus is on the iPad and iPhone but it'll be content accessibility that will help Apple's iOS hardware make further inroads into education and enterprise. Not only that, should Apple finally unveil what Steve Jobs meant when he said he cracked television, the whole iTunes ecosystem is going to be key.
In a few years, we might see iTunes break beyond 10% of Apple's revenue. And should mobile payment become available, regardless of Apple's own take and implementation, watch out.